The present invention relates to a linear, motion drive system in which a moving body or a linear shaft linearly reciprocally moves.
In a conventional linear motion drive system having a moving body linearly reciprocally moving along a linear shaft, e.g., a rail, pressure is applied to the moving body and the linear shaft so as to smoothly move the moving body without looseness.
One of the conventional linear motion drive system is disclosed in Japanese Patent Gazette No. 2002-122136. In the drive system, metal balls are provided between a linear moving body and a linear shaft (a rail) so as to smoothly linearly move the moving body along the linear shaft. To apply pressure to the moving body and the linear shaft, diameters of the balls are slightly greater than a clearance between the moving body and the linear shaft.
By employing the balls disclosed in the Japanese Patent Gazette No. 2002-122136, the clearance between the moving body and the linear shaft can be securely filled with the balls, so that looseness there between can be removed. Therefore, the drive system is capable of suitably linearly conveying a heavy article, whose weight is several hundreds kilogram.
However, in the conventional system disclosed in the Japanese Patent Gazette No. 2002-122136, the diameters of the metal balls are greater than the clearance between the moving body and the linear shaft, so the balls must be deformed. By the deformation of the balls, the balls cannot smoothly roll, so that resistance against the linear motion of the moving body must be great. Thus, a greater power is required to move the moving body. Further, the moving body, the linear shaft and the balls are required to have high abrasion resistance, or they must be hardened. Therefore, manufacturing cost of the drive system must be high, the drive system must be large and heavy, and energy consumption of the drive system must be increased. To smoothly roll the balls and prevent damage of the moving body, the linear shaft and the balls, a large amount of lubricant must be frequently supplied, so that maintenance cost must be high.
In the case of linearly conveying a light article, the large and high cost drive system is not required. For example, a linear motion drive system disclosed in Japanese Patent Gazette No. 7-54843 may be employed. In the drive system, a biasing member, e.g., a coil spring, biases a linear moving body toward a linear shaft, e.g., a linear guide rail. Contact bodies, e.g., lubricant elements, are provided between the moving body and the linear shaft, so that pressure is applied to the linear shaft via the moving body and the contact bodies.
In the drive system disclosed in the Japanese Patent Gazette No. 7-54843, the resistance to the linear motion of the moving body is smaller than that of the drive system disclosed in the Japanese Patent Gazette No. 2002-122136. Therefore, the drive system can be made of light materials, manufacturing cost and maintenance cost of the drive system can be lower.
However, in the drive system disclosed in the Japanese Patent Gazette No. 7-54843, if an external force, which is greater than the elasticity of the biasing member, is applied to the contact bodies, the biasing member is deformed, so that the moving body loosely moves.
To solve this problem, the biasing member having great elasticity, which is greater than a maximum external force expected, was employed to increase the pressure to the linear shaft.
However, it makes frictional resistance between the contact bodies and the linear shaft greater, and the biasing member must be larger. Therefore, manufacturing cost of the drive system must be high, the drive system must be large and heavy, and energy consumption of the drive system must be increased.